Spiral bristled brushes are generally used in the cosmetics industry to apply light weight and medium weight mascara. The spiral brushes work best with the lighter weight, relatively liquid mascara products, which spread somewhat evenly over the bristles for transfer to the eyelashes.
Threaded rod applicators are also known in the cosmetics industry and are used with highly viscous products. These heavy products are carried in the grooves defined by the threads, and eyelashes are dragged over the product, some of which rubs off onto the lashes. Some combing action is achieved, and the combing action becomes more pronounced as the product is used and the grooves become exposed through displacement of the heavy mascara product. However, combing action is limited until enough product is used to more fully expose the screw threads.
As noted above, medium weight, or fixatropic, mascaras can be applied by spiral brush, but the spiral brush has limitations when utilized for that purpose. Thixotropic mascaras are those of medium viscosity, which are flowable but are also capable of assuming and maintaining a three dimentional shape without exterior support. An example of an equivalent weight product is mayonnaise, which can reside in a globule of relatively stable size and dimension, but can also be spread. Some thixotropic mascaras are whipped or aerated, much as whipping cream, and some are gelled.
When thixotropic mascaras are applied to a spiral brush in a container and the brush is removed from the container through a wiper diaphragm, the product is substantially removed from the ends of the brush and is therefore not available for ready application to eyelashes. Thus, a fairly deep combing action may be required to apply the product, and because the product has some tendency to reside in globules, the application may not be uniform. Further, because of the spiral configuration of most brushes, there is a "directional rotation" imparted to the eyelashes, which may cause separation and unevenness where a more parallel orientation is desired.
Thus, neither spiral brushes nor present threaded applicators are fully satisfactory for applying mid-weight cosmetics, and particularly mid-weight thixotropic mascaras.